1. Field of the Invention
The present invention relates to a method and an apparatus for forming an electrode on a part of an end surface, for example, of an electronic component with electrode paste, and more particularly, it relates to a method and an apparatus for applying electrode paste to a portion of an electronic component to be provided with an electrode.
2. Description of the Background Art
Referring to FIG. 9, electrodes 2 are formed on prescribed outer surface regions of an electronic component 1. Each electrode 2 serially extends over an end surface 1a of the electronic component 1 and respective ones of an opposite pair of major surfaces 1b and 1c, which are in series with the end surface 1a through opposite edges of the end surface 1a. Thus, the electrode 2 has a U-shaped section as a whole, and comprises an electrode part 2a which is positioned on the end surface 1a and electrode parts 2b and 2c which are positioned on the major surfaces 1b and 1c respectively.
In general, such electrodes 2 are typically formed by one of the following two methods employing screen printing:
FIG. 10 shows the first method, in which electronic components 1 are received in cavities 11, which are provided in a holder 10, so that upper end surfaces 1a thereof upwardly project from the cavities 11. Screen printing is performed from above the projecting upper end surfaces 1a to form electrode parts 2a. Then, another holder 12 having cavities 13 is prepared as shown in Fig. 11, to receive the electronic components 1 in the cavities 13 in a sidelong manner as shown in FIG. 12. In this state, screen printing is performed on first major surfaces 1b of the electronic components 1, which are in series with the end surfaces 1a, to form electrode parts 2b. Then, the electronic components 1 are so turned over in the cavities 13 as to upwardly direct second major surfaces 1c, and screen printing is performed to form electrode parts 2c.
FIG. 13 shows the second method, in which electronic components 1 are upwardly arranged between a pair of clamp members 15. Similarly to the first method, screen printing is performed on end surfaces 1a of the electronic components 1 to form electrode parts 2a. Then the aforementioned holder 12 is employed to separately perform screen printing on major surfaces 1b and 1c of the electronic components 1, thereby forming electrode parts 2b and 2c respectively.
In the first and second methods, the electrode parts 2a are formed by screen printing in different manners, while the electrode parts 2b and 2c are formed in the same step.
According to the first method, however, as shown in FIG. 14, parts of electrode paste 2d may be adhered to upper edge portions of a pair of walls defining each cavity 11 during screen printing of each electrode part 2a. Such electrode paste 2d may enter the cavity 11 through a clearance defined around the electronic component 1 which is received therein, to stain the electronic component 1. Further, a screen employed for screen printing is pressed by irregular surfaces of the electronic components 1 projecting from the upper openings of the cavities 11 as shown in FIG. 10, and hence the screen is expanded or damaged.
In the second method, on the other hand, electrode paste may cause a capillary phenomenon to enter clearances between the electronic components 1, which are arranged in close contact with each other so that the end surfaces 1a thereof are subjected to screen printing. Thus, the electronic components 1 may be stained by the electrode paste. In order to prevent this, it is necessary to interpose spacers 14 of paper or the like between the electronic components 1, as shown in FIG. 15. However, it takes time to interpose the spacers 14 between the electronic components 1. Also in the second method, the screen for printing is expanded or damaged similarly to the first method.
In addition, the first and second methods commonly have the following disadvantages:
If an end surface 1a of an electronic component 1 to be screen-printed is rounded as shown in FIG. 16, printed electrode paste 2e is irregularized in thickness over the center and end portions along the direction of thickness of the electronic component 1.
Further, the electrode parts 2a, 2b and 2c of the electrodes 2 must be formed in different steps respectively. In order to carry out these steps, it is necessary to transfer the electronic components 1 from the holder 10 or the clamp shown), 15 to the holder 12 and to turn over the same within the holder 12, while drying steps are required after the steps of printing the electrode parts 2a, 2b and 2c respectively. Thus, the operation for printing the electrodes 2 is extremely inefficient.
Each electrode 2 is formed by separately printing the three electrode parts 2a, 2b and 2c, and hence the electrode part 2a may deviate from the electrode part 2b and/or the electrode part 2c (not shown)., as shown in Fig. 17. Such deviation will be further promoted if the screen is expanded or damaged as hereinabove described, for example. The screen may be also expanded or damaged when the same is used over a long period of time.
The electrode paste is exposed to the outside air during the screen printing steps. Thus, viscosity of the paste may be undesirably changed by evaporation of a solvent contained therein. Such change in viscosity of the paste results in change in thickness of a printed paste film. Thus, the printed paste film may be changed in thickness with time during screen printing.